1. Field of The Invention
This invention generally relates to a solid-state laser device which uses laser light emitted by a semiconductor laser as excitation (or pumping) light.
2. Description of The Related Art
A typical example of a prior art solid-state laser device which uses laser light emitted by a semiconductor laser as pumping light is a laser device disclosed in Japanese Unexamined Patent Publication (Kokai Tokkyo Koho) No. 1-166581. Referring to FIGS. 6(a) and 6(b), there is illustrated an optical path of this prior art solid-state laser device. FIG. 6(b) illustrates a view of the optical path on a first plane (namely, the XZ plane (hereunder sometimes referred to simply as a horizontal plane)); and FIG. 6(a) a view of the optical path on a second plane (namely, the YZ plane (hereunder sometimes referred to simply as a vertical plane)).
As illustrated in FIG. 6, in this prior art device, light L.sub.1 (of which the horizontal (X) component is represented by L.sub.1X of FIG. 6(b) and the vertical (Y) component is designated by L.sub.1Y of FIG. 6(a)) to be used for pumping (hereunder referred to simply as pumping light or semiconductor laser light) which is emitted from a semiconductor laser 1 is first changed by a collimating lens 2 into substantially parallel rays. Then, the substantially parallel rays are focused by cylindrical lenses 3a and 3b and made to be incident on a laser medium 4. Thus, the laser medium 4 is excited (or pumped).
Namely, an angle .theta..sub.X of radiation (hereunder sometimes referred to as an emissive angle) of the horizontal (X) component L.sub.1X of the laser light L.sub.1 emitted from the semiconductor laser 1 is different in magnitude from an emissive angle .theta..sub.Y of the vertical (Y) component L.sub.1Y thereof. Therefore, the horizontal (X) component L.sub.1X of the laser light L.sub.1 is focused by the cylindrical lens 3b and on the other hand the vertical (Y) component L.sub.1Y is focused by the cylindrical lens 3a. Thereby, in the laser medium 4, a region SL.sub.1X pumped by the horizontal component L.sub.1X of the light L.sub.1, as well as a region SL.sub.1Y pumped by the vertical component L.sub.1Y thereof, is made to be contained in a region of which the width is equal to a laser oscillation beam width (namely, a laser oscillation beam diameter) WL.sub.2 and the length is equal to that L of the medium 4. Consequently, laser light having good transverse mode characteristics can be efficiently emitted. Incidentally, in FIG. 6, a reflection film 4a formed on an end surface of the laser medium 4 and an output mirror 5 arranged at the other side of the medium 4 forms a laser resonator.
However, in case of the prior art device of FIG. 6, there is necessity of regulating the optical system thereof such that the cylindrical lenses 3a and 3b are placed a predetermined distance apart and further the optical axes of these cylindrical lenses are brought in line with each other and moreover the central axes of the cylindrical surfaces (hereunder referred to as cylindrical axes) of these lenses are perpendicular to each other. Incidentally, in the instant application, an axis composed of the curvature centers of the transverse cross sections of the cylindrical surface of the cylindrical lens is referred to as a cylindrical axis of the cylindrical lens. Thus, this prior art device has drawbacks that the optical system thereof is complex and bulky and that the regulation of the optical system is complicated. Additionally, in case of this device, the number of the surfaces of lenses is larger in comparison with other prior art laser devices. Consequently, the prior art device of FIG. 6 has defects that reflection loss caused at the surfaces of lenses is increased and pumping efficiency is deteriorated. The present invention is accomplished to eliminate the above described drawbacks of the prior art device.
It is accordingly an object of the present invention to provide a solid-state laser device which can be relatively small-sized and easily regulated and emit laser light which excels in excitation (or pumping) efficiency and transverse-mode characteristics.